Technical Field
The present invention relates to a coupled multi-core optical fiber (hereinafter simply referred to as “CMCF”) enabling mode division multiplex transmission while maintaining an optical coupled condition between cores adjacent to each other.
Related Background Art
Japanese Patent Application Laid-Open No. 2011-209702 (Patent Document 1) discloses a technique of reducing transmission loss relating to a multi-core optical fiber (hereinafter simply referred to as “MCF”) in which a plurality of cores are comprised of pure silica glass. Japanese Patent No. 5545236 (Patent Document 2) discloses a technique of reducing transmission loss by adding alkali metal to the core. In addition, Japanese Patent Application Laid-Open No. S60-176004 (Patent Document 3) discloses a structure in which a plurality of single-core fibers can be separated by adopting glass to which alkali metal that is easily melted by acid or the like is added, as glass covering the outermost circumferential surface of the single-core fibers forming a bunch fiber. Tetsuya Hayashi, et al., “Physical interpretation of intercore crosstalk in multicore fiber: effects of macrobend, structure fluctuation, and microbend”, OPTICS EXPRESS Vol. 21, No. 5, pp. 5401-5412 (Mar. 11, 2013) (Non-Patent Document 1) has description relating to transmission loss of an MCF, and Tetsuya Hayashi et al., “Coupled-Core Multi-Core Fiber: High-Spatial-Density Optical Transmission Fibers with Low Differential Modal Properties”, ECOC2015, We. 1. 4. 1. (2015) (Non-Patent Document 2) has description relating to transmission loss of an MCF manufactured by a rod-in collapse method.
Non-Patent Document 1 described above describes the definition of the power coupling coefficient of adjacent cores. Non-Patent Document 2 described above describes a coupled MCF. In addition, R. Ryf, et al., “1705-km Transmission over Coupled Core Fibre Supporting 6 Spatial Modes”, ECOC2014, PD. 3. 2., Cannes-France (2014) (Non-Patent Document 3) discloses a test result of mode division multiplex transmission to which a coupled MCF is applied, and Beril Inan, et al., “DSP complexity of mode-division multiplexed receivers”, OPTICS EXPRESS Vol. 20, No. 9, pp. 10859-10869, (Apr. 23, 2012) (Non-Patent Document 4) discloses a multi-input-multi-output (hereinafter referred to as MIMO (Multi-Input-Multi-Output)) technique to enable mode multiplexing and mode division.